Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 221905
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
205 PM CDT Fri Sep 22 2017

.UPDATE...
1028 AM CDT

Going forecast appears to be in fine shape this morning, and no
changes are needed.

Forecast area remains on western periphery of surface high
pressure ridge, which is centered over the eastern Lakes and Ohio
Valley. Morning RAOBs from DVN and ILX both sampled +20C at H8,
and +25/24C at H9 respectively. Warm start to the morning has
allowed temps to warm into the mid-80`s already as of 10 AM CDT,
and low-mid 90`s appear on track for this afternoon. Weak
southeasterly lake breeze should hold temps down a little along
the immediate Lake Michigan shore. Record high temps of 92 at
Chicago and 93 at Rockford should be withing reach.

Going forecast has this all well in hand. Will freshen text
forecasts late morning for wording, but otherwise no changes
needed at this time.

Ratzer

&&

.SHORT TERM...
341 AM CDT

Through tonight...

Main forecast concerns/challenges are with continued warmth, as
another day of temps well into the 90s are expected today. No big
change in the air mass will support temps similar to Thursday,
with low to mid 90s expected area wide. This will be supported by
an abundance of sunshine, once early morning dense cirrus shifts
to the east. Winds do turn onshore today, but think locations near
the lake will rise to around 90 before this lake breeze cools
temps down some. Dewpoints in the upper 60s will provide another
humid day, with heat index values in the mid to upper 90s. Some
guidance showing some isolated convection developing across the
south/southeast CWA later this afternoon. However, would think
that if anything does develop during this time, that it should
stay just outside of the area.

Rodriguez

&&

.LONG TERM...

Saturday night through Friday...

205 pm...Little change to the forecast for early next week.
Models continue to slowly cool the airmass over the region with
highs falling back into the mid/upper 80s. Sunday still looks to
be mainly sunny and expect several areas to still be able to tag
90. With a bit more cloud cover on Monday...highs likely to stay
in the 80s and there is a chance of showers mainly across far
western IL and likely west of the cwa and chances also remain
below mentionable from this distance. A lake breeze is expected
Sunday and Monday and this will likely keep the IL lakeshore
several degrees cooler once it develops. Patchy fog will also be
possible during the overnight/early mornings through Tuesday.

A cold front will move across the area later Tuesday and Tuesday
night and it had appeared that the precip with this front would be
scattered and short in duration and all the models have trended
that direction. Best chance of precip appears to be across the
northwest cwa Tuesday afternoon/evening and then dissipating as it
spreads southeast. While temps will be much cooler behind this
front...for a day or two...just about back to normal for late
September. A second colder airmass settles across the lakes
region late next week and this will likely push high temps into
the lower/mid 60s. cms

&&

.AVIATION...
For the 18Z TAFs...

Very quiet aviation weather to continue through the next 24-36
hours. Only real concern will be a shift to east-southeast winds
Saturday afternoon, with lake breeze expected to impact Chicago
metro terminals. Only few VFR clouds expected through the period.

In the near term, south winds (generally 190-220 deg) around 10
kts are expected to persist through this afternoon, with the lake
breeze boundary not moving through the terminals.

Ratzer

&&

.MARINE...

205 pm...A large trough of low pressure will remain across the
plains through Monday maintaining southerly flow across Lake
Michigan. This trough/front will move across the region Tuesday
night into Wednesday. High pressure will build across southern
Canada and the northern plains late next week and as the gradient
tightens behind this front ahead of the high...a period of
15-25kts from the northwest is expected. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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